The elevator door machine is a mechanism whose role is to open and close the car door of the elevator hall. When it receives the signals of opening and closing of the elevator door, the elevator door machine controls the door opening motor through its control system to convert the torque generated by the motor into a force in a specific direction to close or open the door. When the preventing closing force exceeds 150N, the door machine automatically stops closing the door and opens the door in the reverse direction to provide a certain degree of door closing protection.
The AC asynchronous variable frequency door machine of the elevator door machine is usually called the variable frequency door machine. Its composition is mainly divided into three parts: the variable frequency door machine control system, the AC asynchronous motor, and the mechanical system; the elevator variable frequency door machine has two motion control methods: speed switch control mode and encoder control mode; speed switch control mode cannot detect the direction, position and speed of the car door, and can only use the position and speed open-loop control, resulting in relatively poor control accuracy. The smoothness of the door machine moving is not very good, so encoder control mode is often used. There are specific elevator door machine inverters available on the market.
The permanent magnet synchronous door machine of the elevator door machine upgrades the AC asynchronous motor to the permanent magnet synchronous motor. A permanent magnet is a method of motor excitation, and frequency conversion is a control method of motor variable speed. In other words, the variable frequency door machine emphasizes that the door machine control part is frequency conversion control, while the permanent magnet synchronous door machine stresses that the door machine motor is a permanent magnet motor. The two technologies of frequency conversion technology and permanent magnet synchronization are complementary to each other.
Permanent magnet low-speed motors have a gear-like rotor structure. Usually, the stator magnetic field rotates once and the rotor magnetic field rotates one tooth. Although low speed can be achieved, the torque is generated by the change of magnetic permeability, and the starting torque and the output per unit volume of the motor are low, and it has its limitations in noise, volume and control accuracy.
The permanent magnet low-speed motor is a motor with carbon brushes, which requires a DC power supply. Its structure is complex and mechanical commutation brings a series of problems, such as the pollution of sparks to the environment, the pollution of carbon powder and the wear of carbon brushes and commutators. These need more frequent maintenance, for their life span is short. Its use on the door opener does not have much advantage over the asynchronous motor plus frequency conversion. The permanent magnet stepper motor operates in an open-loop stepping mode, which is not suitable for low-speed operation of opening and closing doors.
Asynchronous motors have been used indoor openers in the past. Although asynchronous inverters are used, they need to decelerate due to low efficiency, low power factor, small speed range, and inability to achieve constant torque. The innate deficiencies of institutions are contributing to it withdrawing from this field, which is helpless.